Method for disproportionating hydrocarbons

ABSTRACT

THE METHOD OF THIS INVENTION PERMITS DISPROPORTIONATION OF A METHYL BENZENE, SUCH AS TOLUENE, TO FORM A PRODUCT STREAM TYPICALLY CONTAINING BENZENE AND XYLENE   AND THE RECOVERY OF THESE PRODUCTS IN HIGH PURITY.

United Patent:

3,812,197 Patented May 21, 1974 3,812,197 METHOD FOR DISPROPORTIONATING HYDROCARBONS Robert M. Suggitt, Wappingers Falls, and John M. Crone, Jr., Fishkill, N.Y., assignors to Texaco Inc., New York,

' Filed Aug. 25, 1972, Ser. No. 283,678

rm. c1. C07c 3/62 U.S. Cl. 260-672 T 13 Claims ABSTRACT OF THE DISCLOSURE The method of this invention permits disproportionation of a methyl benzene, such as toluene, to form a product stream typically containing benzene and xylene and the recovery of these products in high purity.

FIELD OF THE INVENTION This invention relates to a method for disproportionating hydrocarbons. More particularly it relates to a method for converting a methyl benzene, such as toluene, into high purity benzene with simultaneous production of high quality xylenes.

DESCRIPTION OF THE PRIOR ART As is well known to those skilled in the art, methyl benzenes, typified by toluene, have been disproportionated over various catalysts to produce a product stream containing for example benzene and xylene. Both the lighter benzene stream and the heavier xylene stream contain impurities most commonly including naphthenes and ethyl aromatics. The naphthenes may typically include methyl cyclopentane, cyclohexane, dimethyl cyclopentane, etc. The ethyl aromatics most commonly present may include ethyl benzene in the C fraction and ethyl toluenes in the C fraction.

These impurities are undesirable in that they require substantial processing to remove. For example the treatment of benzene to separate the naphthene fraction (which is necessary to produce high quality benzene) may require extensive fractionation because inter alia the re ported boiling point of benzene is 801 C. and the reported boiling point of e.g. cyclohexane is 80.75 C.

It is an object of this invention to provide a method of disproportionating a hydrocarbon. It is another object of .this invention toconvert a methyl benzene, such as toluene, a benzene and xylene. Other objects will be apparent to those skilled in the art.

. BRIEF SUMMARY OF THE INVENTION In accordance with certain of its aspects, the method of this invention may comprise disproportionating a methyl benzene with hydrogen in the presence of disproportionation catalyst thereby form ing a product stream containing a lower methyl benzene; a methyl benzene, a higher methyl benzene, and a naphthene;

fractionally distilling said product stream thereby separating a lower methyl benzene fraction containing methyl benzene and naphthenes, from a fraction containing higher boiling methyl benzenes;

solvent extracting said lower methyl benzene fraction thereby forming (i) non-aromatic rafiinate containing said naphthene and (ii) aromatic extract containing lower methyl benzene and methyl benzene; and

fractionating said aromatic extract thereby forming (i) as overhead a product lower methyl benzene substantially free of naphthene and (ii) a bottoms.

DETAILED DESCRIPTION OF THE INVENTION The charge methyl benzene which may be disproportionated in accordance with practice of the method of this invention includes monomethyl benzene e.g. toluene, and polymethyl benzenes including xylene, trimethyl benzene, e.g. pseudocurnene, tetramethyl benzenes, etc. Preferably the charge methyl benzene may contain 1-3 methyl groups. The preferred charge methyl benzene may be toluene either substantially pure or more typically in a benzene-toluene-xylene refinery stream.

It will be apparent to those skilled in the art that the charge to the disproportionation operation, a methyl benzene, will be converted to a higher methyl benzene (i.e., a benzene bearing a greater number of methyl groups) and to a lower methyl benzene (i.e., a benzene bearing a lesser number of methyl groups than the charge methyl benzene which latter bears an intermediate number of methyl groups). For example, the charge stream may contain xylenes (dimethyl benzenes); and this may be disproportionated to form a product containing higher methyl benzenes (e.g. trimethyl benzenes) and lower methyl benzenes (e.g. toluene). In the preferred embodiment, the charge methyl benzene may be toluene; and this may be disproportionated to form a product containing a higher methyl benzene (e.g. xylene) and a lower methyl benzene (e.g. benzene per se). For purpose of convenience, this disclosure will refer generally to toluenes as the charge stream; and benzene and xylene will be the principal desired product recovered therefrom.

A typical charge methyl benzene stream which may be treated in practice of the process of this invention may be toluene-containing stream from a catalytic reforming operation. As hereinafter noted, this charge stream may preferably include a recycle stream which contains product benzene from the disproportionation operation.

Preferably this charge stream, prior to disproportionation may be subjected to various processing operations to remove non-aromatics, benzene, and C and higher components. The preferred charge to disproportionation may thus be essentially toluene.

Disproportionating of charge methyl benzene hydro-.

of 05-10, say 4 moles of hydrogen per mole of hydrocarbon over a disproportionation catalyst at 200 C.550,

0., say 280 C. and 50-2000 p.s.i.g., say 800 p.s.i.g.

A typical temperature when a fluorided catalyst is employed, may be 400 'C.-550 C., say 475 C. Typical fluorided catalyst which may be employed may be those disclosed in US. Ser. No. 49,897 filled June 25, 1970 by Robert M. Suggitt, John H. Estes, and Stanley Kravitz (now US. Pat. 3,682,695).

When the disproportionation catalyst is a sulfided catalyst (typically operated at 200 C.-425 C., say 280 C.), there may be added a sulfide such as hydrogen sulfide, methyl disulfide, or as mercaptan. Preferably the sulfide may be added as hydrogen sulfide in amount of 5-100 10- say 20x10* moles of H 5 per mole of hydrogen.

The disproportionation may be effected'at a WHSV of 0.5-10, say 2.5 over a disproportionation. catalyst. Typically the catalyst may contain:

(a) 5-88 parts, say 70 parts, of acid leached mordenite parts, say 15 parts of preferably an alumina gel matrix.

The disproportionation product stream may typically contain as the major components, benzene, toluene, higher methyl benzenes including xylenes, and naphthenes.

In the case of toluene disproportionation for example,

The disproportionation product stream may be condensed and withdrawn from the disproportionation operation and preferably passed to high pressure separation operation wherein hydrogen and hydrogen sulfide are flashed off. The hydrogen and hydrogen sulfide may be recovered; and these gases may be recycled to fresh makeup hydrogen and hydrogen sulfide, compressed to disproportionation pressure, and passed to the disproportionation operation.

The flashed disproportionation product stream, in amount of 2004000 parts, say 1000 parts may be fractionally distilled to separate a benzene fraction from toluene and higher methyl benzenes including xylene. Preferably the separation will permit recovery of at least (i) a benzene fraction, (ii) a toluene fraction, and (iii) a higher methyl benzene fraction including xylene.

In the preferred embodiment, the flashed stream may be heated and passed to a degassing operation wherein remaining gas (hydrogen and hydrogen sulfide) are stripped from the flashed stream.

In one embodiment, the degassing operation may be carried out in a distillation tower, the overhead from which may be condensed. The liquid condensate may be returned to the distillation tower. The non-condensed gases, principally hydrogen and hydrogen sulfide are preferably returned to the disproportionation operation.

The degassing operation bottoms, in amount of 200 4000 parts, say 1000 parts may in one preferred embodiment, include 185 parts of benzene, 547 parts of toluene, 231 parts of xylenes, 34 parts of C and heavier aromatics, and 3 parts of naphthenes and paraffins. This degassed bottoms may be passed to a recycling tower i.e. a tower which, in the preferred embodiment, yields as overhead an impure benzene stream which is preferably combined with fresh charge to the process and recycled to solvent extraction.

Preferably the net overhead from the recycle tower, at 65 C.-l25 0., say 80 C. may include 185 parts of impure benzene which may be recycled to solvent ex traction. Bottoms 812 parts of a toluene-and-heavier fraction are preferably passed to a toluene fractionation operation as set forth infra.

In an alternative embodiment, the overhead from the recycling tower may also include toluene; in this instance the recycling tower bottoms may be passed directly to xylene rectifying operation infra, by-passing the toluene fractionation operation thus resulting, in this embodiment, in one less distillation tower.

In the preferred embodiment, the combined recycled and charge stream may contain 185-4000 parts, say 685 parts of benzene, 200-4000 parts, say 423 parts of toluene, -5000 parts, say 1000 parts of C and greater, principally xylenes, and 100-5000 parts, say 1503 parts of naphthenes. Solvent extraction of this stream to remove non-aromatic components, typically naphthenes such as methyl cyclopentane, etc., may be effected by contact with e.g. sulfolane solvent.

During solvent extraction, the non-aromatics in amount of 100-5000 parts, say 1503 parts remain in the rafiinate which may be withdrawn. The aromatics are found in the extract and, after removal of the solvent, may be found to include -4000 parts, say 685 parts of benzene, 200- 4000 parts, say 453 parts of toluene, 0-5000 parts, say 1000 parts of C and greater.

Aromatic extract may be heated and passed to benzene fractionation operation. Benzene, typically containing less than 0.1% impurities, may be recovered as overhead in amount of 185-4000 parts, say 685 parts. Bottoms,.containing 200-4000 parts, say 453 parts of toluene and 0-5000 parts, say 1000 parts of C and greater, may be heated and passed to a secondary fractionation operation. 2004000 parts, say 453 parts of toluene, withdrawn as overhead from the secondary fractionation operation may be recycled to the disproportionation operation. The C and greater stream (including ethyl benzenes) may be withdrawn as secondary fractionator bottoms in amount of 0-5000 parts, say 1000 parts.

The bottoms from the recycle tower supra may contain 547 parts of toluene, 231 parts of C aromatics including xylenes, and 34 parts of a C and heavier motor naphtha stream. These bottoms may be heated and passed to a toluene fractionation operation. Net overhead may contain 547 parts of toluene which is preferably recycled to disproportion. 265 parts of bottoms from toluene fractionation may be heated and passed to xylene rectifying operation. Rectifier overhead at 138 C.-144 C. may include 231 parts of xylenes containing less than about 1.5% ethyl benzenes. Rectifier bottoms may include 34 parts of a C and greater motor naphtha fraction.

In an alternative embodiment of this invention, it may be possible to achieve many of the advantages of the process of this invention by passing the degassed bottoms from the degassing or stripping operation through a rectifying operation to remove C and heavier as bottoms, the overhead (containing benzene and toluene) being passed directly to the solvent extraction operation. It will be apparent that in this embodiment, it will not be necessary to utilize a separate benzene recycle operation and a toluene fractionation operation, and that the benzene fractionation operation and the secondary fractionation operation will be larger to permit recovery of the streams otherwise recovered in the displaced operations.

it will be apparent to those skilled in the art that the novel process of this invention may be characterized by several desiderata which permit attainment of operations characterized by a high degree of eflijciency.

DESCRIPTION OF A PREFERRED EMBODIMENT Practice of the process of this invention may be apparent to those skilled in the art from inspection of the following description of a preferred embodiment, wherein as elsewhere in this specification, all parts are parts by weight unless otherwise noted. It will be apparent that the drawings are schematic and may not include details of auxiliary processing equipment such as pumps, heat exchangers, collection vessels, etc.

In practice of the process of this invention in accordance with a specific embodiment, there may be admitted through line 10, 1350 parts of a charge stream containing toluene typically as recovered from a catalytic reforming operation. Charge in line 10 may contain the following components:

TABLE II Component Total parts There may be added to the fresh charge in line 10, a recycle benzene-rich stream in line 11, which may contain the following:

TABLE III Component: Parts Benzene 185.0 Toluene 7.0 Naphthenes (C and C 1.4 Paraffins (C to c, 1.6

Total 195.0

TABLE IV Component: Parts Naphthenes 201.4 Paraflins 251.6

The aromatic extract (denuded of solvent which latter is schematically shown as leaving through line 16), containing the benzene fraction and the higher alkyl benzene fraction, in total amount of 1092 parts is withdrawn through line 17; this extract is heated in heat exchanger 18 by steam in line 19 and passed into benzene fractionator 20. Overhead is passed through line 21 to condenser 22 cooled by water in line 23. Condensate is passed through line 24 to condensate drum 25; and thence pumped reflux is passed through lines 26 and 27 to benzene fractionator 20. Product withdrawn through line 28 is 360 parts of high purity benzene containing less than 0.1% of impurities.

Benzene fractionator bottoms are reboiled in reboiler circuit including heat exchanger 29 heated by steam in line 30. 732 parts of benzene fractionator bottoms, recovered through line 31, contain the following:

TABLE V Component: Parts Aromatics:

Toluene 460 C aromatics 225 C and greater 47 Benzene fractionator bottoms are passed through line 31, heated in heat exchanger 32 by steam in line 33 and passed to secondary fractionator 34. Fractionation in secondary fractionator 34 produces bottoms which are principally C C and heavier.

Secondary fractionator bottoms are reboiled in reboiler circuit including heat exchanger 35 heated by steam in line 36. Net bottoms, withdrawn through line 37, have a composition as follows:

TABLE VI Component: Parts C aromatics 225 C and greater 47 Secondary fractionator overhead is withdrawn through line 38 and passed through condenser 39 cooled by water in line 40; the condensate is passed through line 41 to condensate drum 42 from which it is withdrawn through line 43. Pumped reflux is returned through line 44; and net product overhead contains 460 parts of toluene.

The net product overhead in line 45 is passed to line 46 wherein it is preferably combined with toluene fractionator overhead returned through lines 47 and 48 and with hydrogen and hydrogen sulfide returned through line 49. The disproportionation operation charge (methyl benzene charge) in line 46 may contain hydrogen in. a ratio of 4 moles of hydrogen per mole of total toluene feed 6 and 2 parts of hydrogen sulfide together with 1000 parts of toluene feed.

Dispro'portionation operation charge in line 46' at 286 C. and 800 p.s.i.a. including hydrogen and hydrogen sulfide is admitted to disproportionation operation 50 wherein it contacts disproportionation catalyst. Catalyst is a mixture of alumina and a cobalt and aluminumim-pregnated mordenite prepared as follows:

2000 parts of a commercially available sodium mordenite powder having an average particle size of about 10-30 microns and comprising 6.86% Na O, 10.2% A1 0 68.2% S102, and having a SiO A1 0 mole ratio of 11.4/1 was acid leached with 4000 parts of 6 N HCl for 24 hours at a temperature of 130-140 'F. The acid was decanted and the solids washed three times with 4000 parts of hot water and three times with 4000 parts of cold water which provided a product comprising 0.95% Na O, 6.9% A1 0 86.1% SiO and a Slog/A1203 mole ratio of 21.2/ 1. The acid leaching was again repeated, the product was washed free of chloride ion, dried at 300 F. and calcined to a temperature of 1000 F. in a stream of dry air. The final acid leached mordenite consisted of 0.09% Na O, 3.74% A1 0 88.2% SiO and a SiO /A1 O mole ratio of 40/ 1.

410 parts of the acid leached mordenite was impreghated with 250 parts of a cobalt nitrate solution containing parts of Co (NO .6H O; and the impregnated powder was dried for 16 hours at a temperature of to F.

368 parts of Al (S0 .18H O were dissolved in 3000 parts of distilled water; and 300 parts of concentrated ammonium hydroxide were added to elfect precipitation of aluminum hydroxide. The precipitate was recovered by filtration and washed 3 times with distilled water. The cobalt impregnated acid leached mordenite was mixed with the wet hydrated alumina precipitate and passed through a mill to effect homogeneous mixing. After partially drying the mixture at a temperature of 130 to 140 F. for 16 hours and extruding into inch pellets, the pellents were dried at room temperature for 16 hours, at 130 to 140 F. for 8 hours, at 300 F. for 16 hours and finally calcined at 1000 F. for 2 hours in dry air. The calcined catalyst pellets were sulfided at 700 F. for 4 hours with hydrogen sulfide. The recovered sulfided catalyst consisted of 4.4% cobalt, 15% gamma alumina, and the remainder hydrogen mordenite having a SiO /Al O mole ratio of 40/ 1. The composite catalyst had an average crush strength of 20 pounds as determined by using a Chatillon Crush Strength Tester.

The disproportionation product stream in line 51 is passed to high pressure separation or flashing operation 52 wherein hydrogen and a portion of the hydrogen sulfide are withdrawn through line 53 and passed to line 54 where they are mixed with makeup hydrogen and hydrogen sulfide admitted through line 55 The mixed gases are moved by compressor 56 to line 49.

High pressure separator flashed bottoms have the following composition:

TABLE VII Component: Parts Aromatics:

Benzene Toluene 547 Xylene 231 C and greater 34 C and Cr, naphthenes 1.4 C to C parafiins 1.8 Hydrogen sulfide 1.0

This stream in line 57 is heated in heat exchanger 58, by steam in line 59, and passed to degassing operation 60. Overhead in line 61 including a portion of the hydrogen sulfide, some hydrogen, and benzene, is passed through condenser 62 cooled by water in line 63 and passed through line 64 to collection drum 65. 1 part of hydrogen sulfide and 0.2 parts of propane and butanes are withdrawn as non-condensed gas through line 111 and optionally passed to line 55 or more preferably routed to fuel. Benzene condensate is returned to degassing tower 60 through line 66.

Degassing operation bottoms are reboiled in heat exchanger 67 heated by steam in line 68; and net degassed bottoms withdrawn through line 69 include a degassed disproportionated stream having the composition set out in the following table:

TABLE VIII Component: Parts Aromatics:

Benzene 185 Toluene 547 Xylene 231 C and greater 34 C and C naphthenes 1.4 and C paraflins 1.6

Degassed bottoms in line 69 are passed through heat exchanger 70 heated by steam in line 71 and thence to recycling tower 72. Overhead is passed through line 73 to condenser 74 cooled by cooling water in line 75, the condensate passing through line 76 to collection drum 77.

A portion of condensate is returned through line 79 as pumped reflux; and a portion is returned as recycle stream through line 11 to solvent extraction operation 13.

Bottoms from recycling tower 72 may be reboiled in heat exchanger 80 heated by steam in line 81. Net bottoms in amount of 805 parts, withdrawn through line 82 may principally contain toluene, xylene and C and heavier cuts and more specifically have the following composition:

TABLE X Component: Parts Aromatics:

Benzene Toluene 40 Xylene 231 C and greater 34 The stream in line 82 is heated in heat exchanger 83 by steam in line 84 and passed to toluene fractionation operation 85. Overhead in line 86 is condensed in heat exchanger 87 cooled by water in line 88 and passed through line 89 to collection drum 90. Of the condensate in line 91, a portion is passed as pumped back reflux through line 92 to toluene fractionator 85; and a portion is recycled through line 47 to disproportionation operation 50.

Toluene fractionator bottoms are reboiled in heat exchanger 94 heated by steam in line 95. Net bottoms in amount of 265 parts may have the following composition:

TABLE XI Component: Parts Aromatics:

Xylene 231 C and greater 34 Net bottoms in line 96 are heated in heat exchanger 97 heated by steam in line 98 and passed to rectifier 99. Overhead is withdrawn through line 100, condensed in heat exchanger 101 cooled by water in line 102, and passed through line 103 to collection drum 104. A portion of the condensate is passed through lines 105 and 106 as pumped back reflux to rectifier 99. Net overhead product,

s withdrawn in amount of 235 parts through line 107, a xylene fraction, has the following composition:

TABLE XII Component: Parts Ethyl benzene 2 Paraxylene 57 Meta xylene 127 Ortho xylene 49 Rectifier bottoms are reboiled in heat exchanger 108 heated by steam in line 109. Net bottoms in amount of 34 parts are withdrawn through line 110-a motor naphtha having the following composition:

TABLE XIII Component: Parts Ethyl toluenes 2 Mesitylene r 8 Pseudocumene 21 Hemimellitene 2 C aromatics 1 Although this invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention.

We claim:

1. The method which comprises disproportionating a methyl benzene in the presence of hydrogen and a disproportionation catalyst thereby forming a product stream containing a lower methyl benzene, a methyl benzene, a higher methyl benzene, and naphthene;

fractionally distilling said product stream thereby separating a lower methyl benzene fraction containing methyl benzene and naphthenes, from a fraction containing higher boiling methyl benzenes;

solvent extracting said lower methyl benzene fraction thereby forming (i) non-aromatic raflinate containing naphthene and (ii) aromatic extract containing lower methyl benzene, and methyl benzene; and

fractionating said aromatic extract thereby forming (i) as overhead a product lower methyl benzene substantially free of naphthene and (ii) a bottoms.

2. The method as claimed in claim 1 wherein said methyl benzene is toluene.

3. The method as claimed in claim 1 wherein bottoms from said fractionation of aromatic extract are further fractionated to yield a methyl benzene overhead, at least a portion of which is recycled to said disproportionating operation.

4. The method of preparing benzene of high purity as claimed in claim 1 which comprises disproportionating toluene with hydrogen in the presence of disproportionation catalyst thereby forming a product stream containing benzene, toluene, xylene, and naphthene;

fractionally distilling said product stream thereby separating as overhead a benzene fraction containing benzene and naphthene, and as bottoms a fraction containing xylene and naphthene;

solvent refining said overhead benzene fraction thereby forming (i) a non-aromatic raflinate containing said naphthene and (ii) an aromatic extract containing benzene; and

fractionating said aromatic extract thereby forming (i) as overhead a product benzene substantially free of naphthene and (ii) a toluene-containing bottoms.

5. The method of preparing benzene of high purity as claimed in claim 4 including the further step of admitting to said solvent refining operation, fresh charge containing benzene and toluene.

6. The method of preparing benzene of high purity as claimed in claim 4 including the steps of further distilling said toluene-containing bottoms thereby forming a toluene overhead; and

recycling at least a portion of said toluene overhead to said disproportionation operation.

7. The method of preparing benzene from a charge stream containing benzene, toluene, naphthenes, and heavier fractions which comprises solvent refining said charge stream thereby separating said naphthenes from a refined charge stream of arcmatic extract;

fractionating said aromatic extract thereby forming as overhead a product benzene substantially free of naphthene and a bottoms containing toluene and heavier fractions; fractionating said bottoms thereby forming as overhead toluene and as bottoms heavier fractions;

disproportionating said overhead toluene in the presence of disproportionation catalyst thereby forming a product stream containing benzene, toluene, higher alkyl benzene, and naphthene;

fractionally distilling said product stream thereby forming as overhead a stream containing benzene and toluene and as bottoms a stream containing C and heavier hydrocarbons;

passing said overhead stream to said solvent refining operation; and

rectifying said bottoms containing C and heavier hydrocarbons thereby separating xylene overhead and a naphtha bottoms.

8. The method of preparing benzene as claimed in claim 7 wherein said fractionally distilled overhead stream containing benzene and toluene is further fractionated to yield (i) benzene overhead which is passed to said solvent refining operation and (ii) a bottoms containing toluene and heavier components.

9. The method of preparing benzene as claimed in claim 8 wherein said bottoms containing toluene and heavier components are fractionated to yield (i) a toluene overhead which is recycled to the disproportionation operation and (ii) a bottoms containing xylene and C and heavier components.

10. The method of preparing benzene as claimed in claim 9 wherein said bottoms containing xylene and C9 and heavier components are fractionated to yield a high purity xylene product.

11. The method of preparing benzene of high purity which comprises disproportionating toluene in the presence of hydrogen and, as disproportionation catalyst, an acid leached mordenite on which is deposited a Group VIII metal, admixed with alumina, thereby forming a product stream containing benzene, toluene, xylene, and naphthene;

fractionally distilling said product stream thereby separating a benzene fraction containing toluene and naphthene and a fraction containing xylene and toluene;

solvent refining said benzene fraction thereby forming (i) a non-aromatic raffinate containing said naphthene and (ii) an aromatic extract containing benzene and toluene; and fractionating said aromatic extract thereby forming (i) as overhead a product benzene substantially free of naphthenes and (ii) a toluene-containing bottoms further distilling said toluene-containing bottoms thereby forming a toluene overhead; and

recycling at least a portion of said toluene overhead to said disproportionation operation.

12. The method of preparing benzene of high purity as claimed in claim 11 wherein said Group VIII metal is nickel or cobalt.

13. The method of preparing benzene of high purity as claimed in claim 11 wherein said Group VIII metal is nickel or cobalt, said metal being in the form of a sulfide.

References Cited UNITED STATES PATENTS 3,598,879 8/1971 Kmecak et a1. 260-672 T 3,529,031 9/1970 Otani et a1 260-672 T 3,433,735 3/1969 Broughton 260-674 SE 3,476,821 11/ 1969 Brandenburg et al. 260-672 T CURTIS R. DAVIS, Primary Examiner U.S. Cl. X.R. 260-674 SE 

